Single quantum filtering

The mandibular salivary glands (ca. 0.25 g) were isolated and perfused arterially with a modified Krebs solution. Na NMR spectra were collected at 8.4, 4.7 and 2.34 T by using MSL-100, AM-200wb and AMX-360wb, respectively. The T2 double-quantum filter and Tj double-quantum filter were used. Results are summarized in brief 1) The transverse relaxation rate constants showed a slight Bq dependency, which promises a poor fitting by the single population model. 2) When temperature was decreased (37 - 5°C), the ratio of the relaxation... 

By allowing multiple-quantum coherence to process during the evolution period of a two-dimensional experiment, Drobny et al. were able to detect its effects indirectly. This idea subsequently blossomed into the new technique of filtration through double-quantum coherence. Multiple-quantum coherence of order n possesses an n-fold sensitivity to radiofrequency phase shifts, which permits separation from the normal single-quantum coherence. This concept inspired the popular new techniques of double-quantum filtered correlation spectroscopy (DQ-COSY) and the carbon-carbon backbone experiment (INADEQUATE), both designed to extract useful connectivity information from undesirable interfering signals. 

Finally, the very recently proposed double-quantum (DQ) and double-quantum filtered (DFQ) STMAS experiments [42] allow filtering out diagonal (and outer satellite transitions) peaks of STMAS spectra with no loss on sensitivity. The experiments efficiently convert inner ST coherences from single to doublequantum with a central-selective transition 71 pulse. The conversion allows the selection of double-quantum transfer pathways with phase cycling, filtering out the unwanted peaks. 

Traditionally, homonuclear 2D double quantum filtered correlation spectroscopy (DQF-COSY) and total correlated spectroscopy (TOCSY) spectra are valuable in the identification of resonances of individual monosaccharide units. In the presence of small couplings, through space connectivities detected by NOESY/ROESY (nuclear Overhauser effect spectroscopy/ rotational nuclear Overhauser effect spectroscopy) experiments are also useful in completing the resonance assignment. When the H NMR spectra of complex oligosaccharides are too crowded to fully elucidate the structure by homonuclear correlation methods, it is efficient to use 2D heteronuclear correlation methods, such as heteronuclear single quantum correlation... 

A new approach to combining CP with MQ MAS in a 2D NMR experiment has been demonstrated, involving CP from H to the single-quantum coherences of a quadrupolar nucleus.In two separate methods, pure-absorption line shapes have been obtained using a z-filter and a reversed split-ti method. 

The selectivity of multi-quantum filters is demonstrated in Fig. 7.2.28 by spectra recorded for poly(isoprene) (PI) with the multi-quantum filter from Fig. 7.2.26(d) [Schl 1, Schl2, Schl3]. The conventional single-quantum H NMR spectrum of PI shows a broad line with little to no chemical-shift resolution. But the double- and triple-quantum filtered spectrum of the material exhibit peaks at different chemical shifts which can be assigned primarily to the signals from CH2 and CH3 groups, respectively. At longer... 

The use of multi-quantum imaging inherently includes a multi-quantum contrast filter in the sequence. Such multi-quantum filters (cf. Section 7.2.10) can also be combined with single-quantum space encoding techniques. They are used to discriminate coupled spins i from uncoupled spins in liquids and signals from ordered materials from those of disordered materials. 

This concept was extended by Carravetta et al46 to larger spin systems. Iterative analysis of the symmetry-selected, MQ-filtered single quantum spectra of spin systems up to eight spins (/ = 1/2) has been used to determine dipolar coupling constants of molecules aligned in liquid crystalline... 

Fig. 9. Single- and triple-quantum filtered 87 Rb spectra as a function of BSA concentration. The triple-quantum creation time was set to rmax for each sample. The triplequantum filtered spectrum (10240 scans) is plotted above the corresponding singlequantum spectrum (64 scans). The downfield peak in the single-quantum spectrum is a Rb and KI reference. From Ref. 72, with permission.

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